A stochastic model to estimate worm burdens and associated risk factors in sheep naturally infected with Haemonchus contortus

Risk can be defined as the possibility of loss or injury coupled to the probability of such loss or injury (Singh 2000), and the main components of risk analysis are risk assessment, risk management and risk communication (Thrusfield 2001). Quantitative risk assessment is defined as a mathematical model containing inputs and outputs which are expressed numerically (Murray 2004). The work in the present chapter is concerned with the risk assessment part of risk analysis, as it is concerned with hazard identification, and estimation of the probability and magnitude of the risk of haemonchosis as indicated by simulating worm counts in sheep infected with H. contortus.